Figure 4.
In quantum dot detectors, a colloidal thin film of nanocrystals overlays nanowire circuitry. The conductors establish electric field gradients that collect the electrons and holes generated by photons.

Techno-junkies were thrilled five or six years ago when they could buy a mobile phone with a VGA camera, even though they probably had a 5 Mpix digital still camera (DSC) at home. Today, you can walk into nearly any electronics store and buy a smart phone with a 5 Mpix camera inside. “The market has dramatically evolved,” says Venkat Puntambekar, director of marketing for mobile imaging at Aptina Imaging Corp. (San Jose, Calif.). “There is an 18-month pixel shrink span and then every 12 to 18 months the resolution bumps up.” The market for those sensors is slated to reach $2.2 billion in 2010, according to Tom Hausken, director of components practice at Strategies Unlimited (Mountain View, Calif.). Despite the challenges of the application—and those challenges are many—mobile phone camera performance continues to rise (see Figure 1).

Surveys have shown that people use mobile phone cameras most often at night, in bars, frequently after having a few drinks. At first blush, that would seem to reduce performance demands—after all, how high-quality does a photo of your buddy Joe toasting your winning softball team need to be?

The reality is that the application demands high performance under the worst possible conditions. Nightclub lighting is notoriously dim, which requires an image sensor with ultra high dynamic range. In addition, the camera needs to be power efficient, lightweight, robust, and compact enough to fit today’s small form factors. Taken on the whole, the mobile phone application makes building a module for a digital still camera look like a walk in the park. Somehow, though, designers keep rising to the occasion.

“This year, 3 and 5 Mpix will be mainstream,” says Puntambekar. “In Japan, maybe 30 percent of the market is 8 Mpix, but in the rest of the world, that’s still very much a niche market. Next year we’ll even see a few 12 Mpix. What happens after that is anybody’s guess.”

Zooming In

If the average smart phone user lacks the equipment to print an image larger than 5 Mpix, what benefits do manufacturers hope to gain by producing camera modules with resolutions two and three times that? The answer lies not in pictures but in non-imaging capabilities like visual search and zoom.